Polymeric coating compositions, polymer coated substrates, and methods of making and using the same

ABSTRACT

This invention relates to a coated substrate comprising (i) a substrate and (ii) a coating thereupon comprising a polymeric composition formed from (a) twenty-five to ninety-nine parts by weight of a poly(amide-imide) prepolymer; (b) one to twenty-five parts by weight of a trifunctional ester selected from the group consisting of trifunctional methacrylate ester, trifunctional acrylate ester, and mixtures thereof; (c) from 0.5 to fifteen parts by weight of an organo-reactive silane consisting of an amino group containing alkoxysilane having the formula NH 2 (CH 2 ) n Si(OC 2 H 5 ) 3  where n is an integer from one to twenty; and (d) a conductive additive.

RELATED APPLICATION

This application is a division of application Ser. No. 09/087,536 filedMay 29, 1998, which application is hereby incorporated in its entiretyby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates broadly to polymeric coating compositions suitablefor providing a coating which is solderable and/or has high corrosionresistance and to substrates coated with the same. The coated substrateshave improved properties, most importantly, resistance to hostileenvironments such as corrosive liquids and gases. Furthermore, thecoated substrates the ability to be soldered without breaching thepolymeric coating and/or electroplated. The invention further relates tomethods for producing the polymeric coating compositions and polymercoated substrates.

2. Description of the Related Art

Several publications are referenced in this application. Thesereferences describe the state of the art to which this inventionpertains, and are incorporated herein by reference.

Polymers have been grafted onto metallic substrates to form coatingsthat protect the substrates from a variety of environmental conditions.Typically organic coatings and paints are applied onto metallicsubstrates via a physical bond and act to protect the substrate fromcorrosive gases, solutions of high or low pH, varying relative humidityand varying temperature conditions. Such physically bonded coatingstypically do not provide adequate protection against corrosion or otherenvironmental impacts and have a tendency to become dislodged from thesurface of the substrate after relatively short periods of time,particularly under stresses imposed by severe environmental conditions,e.g. the presence of acids or bases, corrosive gases such as hydrogensulphide, sulphur dioxide and carbon dioxide.

Metal substrates have been coated with polymers by graft polymerizationprocesses with results that are superior to those obtained where themetal substrate is coated with organic paints or coatings. Such graftedcoatings are both conductive and provide a durable protective layerwhich is resistent to severe environmental conditions. U.S. Pat. No.5,043,226 to Wiedeman, et al. describes methods for applying graftpolymers to a variety of metal substrates such as steel, aluminum, ironand other metals.

It is important in many applications that the metal coated substratehave not only excellent corrosion and abrasion resistance as well asresistance to adverse environmental conditions, but that the coatedmetal also have satisfactory conductivity and solderability, so that itcan be used in a variety of industrial applications. Heretofore, the arthas not provided polymer coated metal substrates having both atenaciously bound polymer layer which is corrosion resistant and thenecessary properties of conductivity and solderability.

OBJECTS OF THE INVENTION

It is an object of the invention to overcome the above-identifieddeficiencies.

It is a primary object of this invention to provide a polymer coatingcomposition for a substrate wherein the polymer is grafted to thesubstrate and tenaciously bound thereto.

It is a further object of the invention to provide a polymer-coatedsubstrate which is highly resistant to abrasion and corrosion as well asto a variety of hostile environmental conditions, including humidity,temperature, pH, chemical attack, etc.

It is still a further related object of this invention to provide apolymer-coated substrate in which the polymer-coating is tenaciouslybound to the metal substrate and does not admit of bubbling, cracking orother failure which exposes the substrate to environmental conditions,and, which further has satisfactory conductivity and solderabilitycharacteristics such that a metallic or non-metallic substrate, forexample, can be used in a variety of industrial applications.

It is still a further and related object of this invention to provide amethod for producing such polymer-coated substrates.

It is still a further and related object of this invention to providesuch a process wherein the polymer-coating can be relativelyinexpensively applied to a variety of substrates.

The foregoing and other objects and advantages of the invention will beset forth in or apparent from the following description.

SUMMARY OF THE INVENTION

The invention relates to novel polymeric coating compositions suitablefor coating substrate materials. The polymeric composition according tothe invention comprises:

(i) from 25 to 99 parts by wt of a poly(amide-imide) prepolymer;

(ii) from 1 to 25 parts by wt of trifunctional ester, preferably amethacrylate ester of the formula:

(iii) from 0.5 to 15 parts by wt of a organo-reactive silane monomer,preferably an organo-reactive silane of the formula:

H₂N(CH₂)_(n)Si(OC₂H₅)₃

wherein n is an integer from 2 to 20.

According to one preferred embodiment, the coating is a conductivecoating comprising conductive additives.

Surprisingly, it has been found that the polymer composition can beapplied to a variety of substrates including steel, stainless steel,iron, brass, copper, aluminum, platinum, titanium, silver, gold, Telfon,plastics, glass and others, and that the coated substrate has bothexcellent resistance to abrasion and corrosion as well as highlydesirable properties of conductivity and solderability. Thus, the coatedsubstrates can be used in a variety of products which are exposed tohostile environmental conditions (including high humidity, temperatures,pressures and corrosive gases) while being fabricated into varioussub-components and packaging.

For example, it has now been found that polymer-coated componentsproduced according to the invention can be soldered directly through thepolymer coating without breaching that coating and exposing theunderlying substrate to environmental conditions. This is a vastimprovement over prior art practices which required that the polymercoating be scraped away to expose the substrate to the soldering orwelding operation.

The coated substrates in the invention can be efficiently andeconomically prepared by a graft polymerization procedure which includesthe steps of:

(a) forming a prepolymer mixture comprising:

(i) from 25 to 99 parts by wt of a poly(amide-imide) prepolymer;

(ii) from 1 to 25 parts by wt of a trifunctional ester; and

(iii) from 0.5 to 15 parts by wt of an organo-reactive silane;

(iv) a solvent for said components (i)-(iii); and

(v) an effective amount of nickel powder;

(b) applying said prepolymer mixture to the surface of said substrate;and

(c) curing said prepolymer mixture.

Accordingly, the invention also relates to a coated substrate comprisinga substrate and a polymeric coating thereupon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The polymeric coating composition of the present invention is comprisedof three different monomeric units, at least one poly(amide-imide)prepolymer, at least one trifunctional ester and at least oneorgano-reactive silane.

The composition is formed by forming a mixture of monomers containingall three of the aforedescribed components. Broadly, the mixturecontains from 25 to 99 parts by wt of the poly (amide-imide) prepolymer,from 1 to 25 parts by wt of the trifunctional ester, and from 0.5 to 15parts by wt of the organo-reactive silane. Desirably the mixturecontains from 70 to 99 parts by wt of the poly (amide-imide) prepolymer,from 5 to 20 parts by wt of trifunctional ester and from 0.5 to 5 partsby wt of the organo-reactive silane monomer. Best results are obtainedwhere the polymeric composition comprises from 85 to 95 parts by wt ofthe poly (amide-imide) prepolymer, from 5 to 15 parts by wt of the esterand from 1 to 5 parts by wt. of the silane.

The major component of the polymeric composition is a reactive poly(amide-imide). The monomer is fairly low in molecular weight and isreadily soluble in organic solvents. The poly (amide-imide) may be, forexample, composed of trimellitic, aromatic amide and aromatic imidemoieties. AMOCO Al-10 Polymer, available from AMOCO Oil Company, is asuitable component. As supplied, Al-10 Polymer is approximately 50% inthe un-imidized or amic acid form. These two-forms of polymer are shownbelow:

Other suitable polyamides-imides are set forth in U.S. Pat. No.4,316,974 to Ohmura et al. and U.S. Pat. No. 5,087,658 to Nishizawa etal.

The reactive poly (amide-imide) is soluble in a number of solvents. Whenpolymerized as a homopolymer, the solution of the monomer is heated toachieve drying and cure. During such polymerization steps the solvent isremoved, the amic form is cyclisized to the amide-imide form and bychain extension the molecular weight of the polymer increases.

Details of the imidization reaction and the temperature and solventconditions associated therewith are given in Application Bulletin AMOCOAl-10 Polymer, hereby incorporated by reference.

The second monomer is a trifunctional ester. Suitable trifunctionalesters include those known in the art including methacrylate ester,acrylate ester, acid ester and mixtures thereof.

According to one preferred embodiment of the invention, thetrifunctional ester is a trifunctional methacrylate ester preferablyhaving the formula:

A suitable trifunctional methacrylate ester is SR 9011 available fromSartomer.

The third monomer, used in the smallest amount, is an organo-reactivesilane which acts as an adhesion promotor. According to one preferredembodiment, the organo-reactive silane is a silane having the formula:

NH₂(CH₂)_(n)Si(OC₂H₅)₃

wherein n is an integer from 1 to 20, preferably 2-10.

According to another preferred embodiment, the silane is anaminoalkyltriethoxysilane of the formula:

NH₂(CH₂)₃Si(C₂H₅)₃.

A suitable silane of the above-formula can be obtained under designationA-1100 from OSi Specialties, Inc., 39 Old Ridgebury Road, Danbury, Conn.06817-0001. The compound sold under that designation is3-aminopropyltriethoxysilane. Technical details relating to A-1100 maybe obtained in Table (i) Dow Corning Brand Organo-Reactive Silanes.

Another aspect of the invention relates to substrates coated with thepolymeric composition of the invention. The metal substrates which canbe coated according to the invention include steel, iron, aluminum,brass, copper, platinum, titanium, gold, silver and other metals.Plastics can also be coated using the invention. Surprisingly, thecoating composition is able to adhere to teflon. The two importantcriteria of the substrate is (1) that it is wettable by the polymercomposition and (2) can withstand the curing temperatures used to curethe coating (as high as 200 to 300° C.). The substrate may be preparedfor coating by dipping, applying, spraying, etc.

A further embodiment of the invention relates to a conductive coatingcomprising the polymeric composition and a conductive additive.Providing a conductive coating allows the coated substrate to be used ina variety of applications. Preferably, the coating compositionscomprises at least 40 parts by wt conductive filler, more preferably atleast 50 parts by wt, even more preferably at least 60 parts by wt andmost preferred at least 70 parts by wt.

According to one embodiment, the coating has sufficient conductivity toallow for soldering and/or electroplating. Surprising, not only can thecomposition be coated onto materials such as teflon, the resultantcoating can also be soldered and/or electroplated.

Preferably, the coating has a surface resistivity less than 5 ohm persquare, more preferably less than 2 ohm square, even more preferablyless than 1 ohm square and most preferred less than 0.5 ohm per square.If the conductivity of the coating is too low for soldering, the coatingcan be first electroplated and then soldered.

Thus, one embodiment of the invention relates to a conductive polymericcomposition comprising a conductive particulate material. The conductiveparticulate material may comprise powders, flakes, fibers, platelets, ormixtures thereof and may be any conductive material. Preferably, theconductive material does not oxidize. The conductive particulatematerial may comprise metals including nickel, copper, silver, gold,platinum, etc.

According to a preferred embodiment of the invention, the conductiveparticulate material comprises nickel powder. Preferably, the coatingcomposition comprises at least 60 parts by wt nickel powder. Accordingto a still further preferred embodiment of the invention, the conductiveadditive is a nickel powder which not only provides conductivity, butalso acts as a graft initiator. The nickel powder used as a graftinitiator is desirably in finely divided form, eg. at least less than−200 mesh, preferably less than −250 mesh and most desirably less than−325 mesh. A suitable nickel powder may be obtained from Novamet underdesignation Flake HCA-1.

Another aspect of the invention relates to a method of forming thecoating composition of the invention. In order to provide a coatingcomposition comprising the above-identified monomers, the components aredispersed in a suitable solvent. A number of different solvents may beused to dissolve the three monomers to form a prepolymer solution. Amongthese solvents are 1-methyl 2-pyrrolidone, acetone, formamide, dimethylformamide, dimethyl sulfoxide and dimethyl acetamide.

The mixture of monomers and solvents and conductive filler (for aconductive coating) is prepared as follows. The poly (amide-imide)prepolymer is dissolved in 1-methyl 2-pyrrolidone solvent. The solidprepolymer is milled for a time sufficient to dissolve it in thesolution. The mixture is filtered to remove undissolved solids. Thesolution of prepolymer is added to a second solvent comprising anadditional amount of 1-methyl 2-pyrrolidone and Aromatic Solvent 150(Aromatic Solvent 150 has the chemical name solvent naphtha (petroleum),heavy aromatic and is available from Shell Chemical Company). The ratioof the pyrrolidone to the Aromatic Solvent in the second solvent rangesfrom from 10/1 to 1/10. The solution of poly (amide-imide) prepolymer isthen added to the second solvent and that mixture is stirred until thesolution is uniform.

The tri-functional ester (preferably, methacrylate ester), theorgano-reactive silane (preferably, aminoalkyl-triethoxysilane) and theconductive filler (preferably, nickel powder) are then added to thesolution with stirring to form a uniform composition.

The mixture of monomers, solvent and nickel powder formed as describedabove is applied to the metal substrate by spraying while continuouslystirring the solution. The solution may be sprayed by equipment wellknown in the art. Broadly, from 1.0 to 4.0 grams of solution applied persquare cm of metal substrate to achieve a coating from 0.1 to 2.0 milthick. Desirably from 2.0 to 3.5 grams of solution are applied toachieve a coating from 0.5 to 1.0 mil thick and most preferably from 2.5to 3.0 grams per square cm are applied to achieve a coating from 0.5 to0.6 mil thick.

The coated samples are then cured to form the polymeric coating on thesubstrate. Broadly the coated samples are held at a temperature of from100 to 300° C. for from 12 to 15 minutes to permit the solvents to bedriven off and the polymerization and grafting of the polymer on themetal substrate to take place. Preferably the coated samples are curedat a temperature from 200 to 280° C. for from 5 to 10 minutes and bestresults are obtained by curing the coated substrates at a temperature of240 to 250° C. for from 5 to 7 minutes.

EXAMPLES

The following examples are illustrative of some of the products andmethods of making the same falling within the scope of the presentinvention. They are, of course, not to be considered in any waylimitative of the invention. Numerous changes and modification can bemade with respect to the invention.

Example I

Following the procedure described above, a solution of poly(amide-imide)prepolymer (AMOCO Al-10) in 1-methyl 2-pyrrolidone was formed. Thesolution contained 8.10 grams of prepolymer and 24.30 grams of 1-methyl2-pyrrolidone. This solution was added to 11.66 grams of 1-methyl2-pyrrolidone and 4.55 grams of aromatic Solvent 150. To that mixturewas added 1.00 grams of methacrylate ester SR-9011, 0.20 grams of3-aminopropyltriethoxysilane (A-1100) and 80.00 grams of nickel powder(Novamet Flake HCA-1).

The mixture so-formed was continuously stirred and sprayed on a 7 squarecentimeter panel of precleaned steel. 12-14 grams of the mixture wasthus coated on the panel. The coated panel was then cured for fifteenminutes at a temperature of 220° C. to effect polymerization of themixture and grafting thereof to the surface of the panel.

A coated steel is thus obtained. The coating is resistant to corrosiveenvironments and is solderable. The coating had good adhesion(crosshatch, D3359), good abrasion resistance (10 liters sand falling),good impact strength (ASTM D 2794, 100/60 inch pound) and passed 200hours of the Salt Fog ASTM B 117 test. During soldering, the coatingexhibited good adhesion in the flux.

Example II

A coating composition is formed having the following composition:

Ingredients Parts by Weight Polyimid prepolymer Torlone AI10 32.00 25%solution in 1-Methyl 2-Pyrrolidinone 1-Methyl 2-Pyrrolidinone 12.00Aromatic Solvent 150 4.00 Trimethylol Propane Tri Acrylate SR350 1.00Monomer Silane A187 0.20 Nickel Powder Novamet HCA-1 75.00

The mixture so-formed is continuously stirred and sprayed on a panel ofprecleaned steel. The coated panel is then cured for fifteen minutes ata temperature of 220° C. to effect polymerization of the mixture andgrafting thereof to the surface of the panel.

A coated steel is thus obtained. The coating is resistant to corrosiveenvironments and is solderable.

Example III

A soldering iron of 200 watts 1/2″ tip was used for testingsolderability of a coated substrate according to the invention.

A coated metal coupon was taken and the desired flux (in the form of awire—provided by JHR) was melted on the coated surface of the metal withhot soldering iron. The melted flux had good adhesion to the coatedsurface and was used to join two metals together. A non-coated metalliccoupon was not receptive to the adhesion of melted flux. This proves thefact that the coated surface has surprisingly improved solderability.

The above description of the invention is intended to be illustrativeand not limiting. Various changes or modifications in the embodimentsdescribed may occur to those skilled in the art. These can be madewithout departing from the spirit or scope of the invention.

What is claimed is:
 1. A coated substrate comprising: (i) a substrate,and (ii) a coating thereupon comprising the polymeric compositioncomprising: (a) from 25 to 99 parts by weight of a poly(amide-imide)prepolymer; (b) from 1 to 25 parts by weight of a trifunctional esterselected from the group consisting of trifunctional methacrylate ester,trifunctional acrylate ester, and mixtures thereof; (c) from 0.5 to 15parts by weight of an organo-reactive silane consisting of an aminogroup containing alkoxysilane having the formula NH₂(CH₂)_(n)Si(OC₂H₅)₃where n is an integer from 1 to 20; and (d) a conductive additive. 2.The coated substrate of claim 1, wherein said substrate is polymeric. 3.The coated substrate of claim 1, wherein said substrate comprises metal.4. The coated substrate of claim 3, wherein said metal is selected fromthe group consisting of steel, iron, brass, copper, aluminum, platinum,titanium, silver and gold.
 5. The coated substitute of claim 4, whereinsaid substrate is plastic.
 6. The coated substrate of claim 4, whereinsaid substrate is teflon.
 7. The coated substrate of claim 4, whereinsaid coating further comprises further comprises a conductiveparticulate material.
 8. The coated substrate of claim 1, wherein saidconductive particulate material comprises powders, flakes, fibers,platelets, or mixtures thereof.
 9. The coated substrate of claim 1,wherein said conductive particulate material comprises metal.
 10. Thecoated substrate of claim 1, wherein said conductive particulatematerial comprises nickel powder.
 11. The coated substrate of claim 1,wherein said coating comprises 60 parts by wt conductive filler.
 12. Thecoated substrate of claim 1, wherein said coating has a surfaceresistivity less than 2 ohm per square.
 13. A coated substrate formed bya method comprising the steps of: (a) forming a prepolymer mixturecomprising: (i) from 25 to 99 parts by wt of a poly(amide-imide)prepolymer; (ii) from 1 to 25 parts by wt of a trifunctional esterselected from the group consisting of trifunctional methacrylate ester,trifunctional acrylate ester, and mixtures thereof; and (iii) from 0.5to 15 parts by wt of an organo-reactive silane consisting of an aminogroup containing alkoxysilane having the formula NH₂(CH₂)_(n)Si(OC₂H₅)₃where n is an integer from 1 to 20; (iv) a solvent for said components(i)-(iii); and (v) an effective amount of conductive filler; (b)applying said prepolymer mixture to the surface of said substrate; and(c) curing said prepolymer mixture.
 14. A coated substrate comprising:(i) a substrate, and (ii) a polymeric composition applied thereuponcomprising: (a) from 25 to 99 parts by weight of a poly(amide-imide)prepolymer; (b) from 1 to 25 parts by weight of a trifunctional esterselcted from the group consisting of trifunctional methacrylate ester,trifunctional acrylate ester, and mixtures thereof; and (c) from 0.5 to15 parts by weight of an organo-reactive silane consisting of an aminogroup containing alkoxysilane having the formula NH₂(CH₂)_(n)Si(OC₂H₅)₃wherein n is an integer from 1 to
 20. 15. A method for forming thecoated substrate of claim 14 comprising the steps of: (a) forming aprepolymer mixture comprising: (i) from 25 to 99 parts by wt of apoly(amide-imide) prepolymer; (ii) from 1 to 25 parts by wt of atrifunctional ester; (iii) from 0.5 to 15 parts by wt of anorgano-reactive silane; and (iv) a solvent for said components(i)-(iii); (b) applying said prepolymer mixture to the surface of saidsubstrate; and (c) curing said prepolymer mixture.